Colored light is often a blend of different colors. A spectrometer is a device which splits those colors apart, like a prism, and measures the strength of each color. A typical output of a spectrometer looks like this spectrum of the daytime sky, with the actual light spectrum at the top and the graph of wavelength (horizontal axis) and intensity (vertical axis) below:
Types of spectrometry
There are different ways to use spectrometers, and the key difference is how you illuminate your sample.
The first type is fluorescence spectrometry, which is where a high-energy light like an ultraviolet laser is used to excite a sample so that it fluoresces, or glows. It can be used to to identify oil pollution samples. Since different oils fluoresce in different colors, this technique can be used to match an unknown sample with a reference sample to identify it.
Emission spectroscopy is the kind often done in the classroom, where burning a material emits a colored flame. A spectrum of this colored flame can be used to match a material, but it can be unsafe to burn unknown samples, so we have primarily begun to use this technique to attempt to monitor distant flares, for example at gas refineries in Louisiana, to try to detect heavy metals.
Absorption spectroscopy — shining a full-spectrum light like a halogen or incandescent (not a fluorescent or laser) through a sample to see what colors are absorbed — is a bit more difficult in the visible light range, as most of the “fingerprint” features of spectra are too long or too short wavelengths for our webcam-based devices. However, a considerable amount of work has been done on absorption spectrometry of algae, wine, beer, coffee and tomatoes.
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